Not Applicable
1. Field of the Invention
The present invention relates to golf balls and golf ball cover and boundary layer materials. More specifically, the present invention relates to a method to verify the concentricity of a golf ball cover using X-ray imaging of barium doped boundary layer.
2. Description of the Related Art
Conventionally golf balls are made by molding a cover around a core. The core may be wound or solid. A wound core typically comprises elastic thread wound about a solid or liquid center. Unlike wound cores, solid cores do not include a wound elastic thread layer. Solid cores typically may comprise a single solid piece center or a solid center covered by one or more mantle or boundary layers of material.
The cover may be injection molded, compression molded, or cast over the core. Injection molding typically requires a mold having at least one pair of mold cavities, e.g., a first mold cavity and a second mold cavity, which mate to form a spherical recess. In addition, a mold may include more than one mold cavity pair.
In one exemplary injection molding process each mold cavity may also include retractable positioning pins to hold the core in the spherical center of the mold cavity pair. Once the core is positioned in the first mold cavity, the respective second mold cavity is mated to the first to close the mold. A cover material is then injected into the closed mold. The positioning pins are retracted while the cover material is flowable to allow the material to fill in any holes caused by the pins. When the material is at least partially cured, the covered core is removed from the mold.
As with injection molding, compression molds typically include multiple pairs of mold cavities, each pair comprising first and second mold cavities that mate to form a spherical recess. In one exemplary compression molding process, a cover material is pre-formed into half-shells, which are placed into a respective pair of compression mold cavities. The core is placed between the cover material half-shells and the mold is closed. The core and cover combination is then exposed to heat and pressure, which cause the cover half-shells to combine and form a full cover.
As with the above-referenced processes, a casting process also utilizes pairs of mold cavities. In a casting process, a cover material is introduced into a first mold cavity of each pair. Then, a core is held in position (e.g. by an overhanging vacuum or suction apparatus) to contact the cover material in what will be the spherical center of the mold cavity pair. Once the cover material is at least partially cured (e.g., a point where the core will not substantially move), the core is released, the cover material is introduced into a second mold cavity of each pair, and the mold is closed. The closed mold is then subjected to heat and pressure to cure the cover material thereby forming a cover on the core. With injection molding, compression molding, and casting, the molding cavities typically include a negative dimple pattern to impart a dimple pattern on the cover during the molding process.
Materials previously used as golf ball covers include balata (natural or synthetic), gutta-percha, ionomeric resins (e.g., DuPont""s SURLYN(copyright)), and polyurethanes. Balata is the benchmark cover material with respect to sound (i.e. the sound made when the ball is hit by a golf club) and feel (i.e. the sensation imparted to the golfer when hitting the ball). Natural balata is derived from the Bully Gum tree, while synthetic balata is derived from a petroleum compound. Balata is expensive compared to other cover materials, and golf balls covered with balata tend to have poor durability (i.e. poor cut and shear resistance). Gutta percha is derived from the Malaysian sapodilla tree. A golf ball covered with gutta percha is considered to have a harsh sound and feel as compared to balata covered golf balls. Ionomeric resins, as compared to balata, are typically less expensive and tend to have good durability. However, golf balls having ionomeric resin covers typically have inferior sound and feel, especially as compared to balata covers. Polyurethane covered golf balls have greater durability and a better feel than ionomer covers, however, polyurethane is relatively expensive and requires greater skill during manufacturing of the golf ball.
No matter what material is used, one essential requirement for manufacturing a golf ball ,is properly balancing the golf ball to prevent the golf ball from hooking or slicing when in flight after having been hit with a golf club. Further, a golf ball that is not balanced properly will roll out of alignment during putting. The necessity for a properly balanced golf ball is further complicated by multiple piece golf balls, especially golf balls that have a cast thermoset layer. Most thermoset layers are only centered during insertion of the core into the thermoset mixture in the cavity, and thus, the core may move during the casting process. Detection of uncentered golf balls is difficult, and often requires damage to the golf ball itself.
Baryte fillers and other barium containing components have been used in golf balls in the past. Brown, U.S. Pat. No. 2,259,060; Cox et al., U.S. Pat. No. 3,883,145; and Chikaraishi, U.S. Pat. No. 5,609,532, all disclose using barium sulfate, barytes, in the core as a filler for weighting purposes to enhance balancing. Yamada et al., U.S. Pat. No. 4,679,794; Sullivan, U.S. Pat. No. 4,884,814; and Yamada, U.S. Pat. No. 5,274,041, all disclose using barium sulfate as a pigment for use in a golf ball cover, in an amount varying from one to ten parts by weight of the resin. Further, Higuchi et al., U.S. Pat. No. 5,704,854, discloses using barium sulfate as a weight adjusting filler.
However, the prior art fails to disclose a use for determining the concentricity of a golf ball using barium sulfates.
The present invention provides a method for determining the concentricity of a multiple piece golf ball without damaging the golf ball. The present invention is able to accomplish this by providing a golf ball with a doped boundary layer that is imaged in an X-ray machine to measure the concentricity of the boundary layer and cover relative to the core.
One aspect of the present invention is a method for verifying the concentricity of a golf ball cover. The method includes forming a boundary layer over a core. The boundary layer is composed of a polymer material doped with barium or bismuth. Then, a cover is formed over the doped boundary layer to create a covered golf ball. Next, the covered golf ball is placed within an X-ray imaging machine. Finally, the covered golf ball is irradiated within the X-ray imaging machine to image the doped boundary layer relative to the cover and the core to determine the thickness of the cover.
The method also includes rejecting covered golf balls that have an unacceptable cover thickness. The method also includes measuring the thickness of the cover at two or more locations to determine concentricity. The method also includes detecting the outer perimeter of doped boundary layer, detecting the outer perimeter of the cover, and measuring the thickness of the cover.
Another aspect of the present invention is a method for verifying the concentricity of a multiple piece golf ball. The method includes forming a boundary layer over a solid core comprising a polybutadiene material. The boundary layer includes an ionomer blend material doped with barium in an amount of five to fifteen parts per hundred of the ionomer blend material. The method also includes forming a thermoset polyurethane cover over the doped boundary layer to create a covered golf ball. Next, the covered golf ball is placed within an X-ray imaging machine. Finally, the covered golf ball is irradiated within the X-ray imaging machine to image the doped boundary layer relative to the cover and the core to determine the thickness of the cover.
Having briefly described the present invention, the above and further objects, features and advantages thereof will be recognized by those skilled in the pertinent art from the following detailed description of the invention when taken in conjunction with the accompanying drawings.